Recurring fevers: causes, red flags and when to get it checked

Fever is a response to inflammatory chemicals released by infection, immune activation, tissue injury or tumours. A single fever from a viral illness is common. Recurring or prolonged fevers suggest a persistent source, such as a hidden infection, or an inflammatory or tumour process that keeps triggering the response.

• Repeated viral infections, particularly with young children at home.

• Urinary tract infection, chest infection, sinusitis, dental abscess and skin infections.

• Infections after travel: malaria, typhoid, dengue and others, which need urgent assessment.

• Glandular fever (infectious mononucleosis), cytomegalovirus, hepatitis, HIV seroconversion and tuberculosis.

• Endocarditis, abscesses in the abdomen or pelvis, and bone or joint infection.

• Inflammatory diseases: rheumatoid arthritis, lupus, vasculitis, giant cell arteritis, inflammatory bowel disease and adult-onset Still disease.

• Autoinflammatory and periodic fever syndromes, such as familial Mediterranean fever.

• Lymphoma, leukaemia, kidney cancer and other cancers; drug fever and blood clots.

Fever with rash, stiff neck, confusion, rapid breathing, low blood pressure, severe headache, shaking chills, new heart murmur, recent travel to malarial areas, immunosuppression, weight loss, night sweats, lumps, bone pain, a prosthetic joint or heart valve, or intravenous drug use warrants urgent review.

• Call 999: fever with a rash that does not fade under a glass, severe headache with stiff neck, confusion, difficulty breathing or collapse.

• Same-day GP or NHS 111: fever after travel, with shaking chills, or in someone on chemotherapy or immunosuppressants.

• GP within days: fever persisting more than three to five days, or recurring fevers with weight loss or sweats.

• Routine: a single fever with a cold that settles.

The doctor asks about the pattern, duration, travel, contacts, animals, occupation, dental problems, urinary and chest symptoms, rash, joint pain, weight loss, sweats, medicines, sexual history and immune status. They examine the skin, mouth and teeth, glands, heart, chest, abdomen, joints and look for new murmurs.

• Full blood count, CRP, ESR, liver and kidney function, and blood cultures.

• Urine tests and chest X-ray: to look for common infection sources.

• Serology for glandular fever, HIV, hepatitis, tuberculosis testing and other infections guided by history.

• Autoimmune tests such as ANA and rheumatoid factor; ferritin and LDH.

• CT or PET-CT scans, echocardiography and biopsies for persistent unexplained fever.

Rest, drink plenty of fluids and take paracetamol or ibuprofen if suitable. Keep a temperature chart with times, and note rashes, sweats and joint symptoms. Avoid unnecessary antibiotics before cultures if you are stable, as they can mask diagnosis. Complete any prescribed treatment.

The NHS route is a GP, then hospital assessment or specialist clinics for persistent fevers. Private infectious disease, rheumatology and haematology consultations offer direct access to tests and imaging.